This invention relates to photographic apparatus and particularly to an automatic focusing system for a camera. The present invention is an improvement over the "Nodal Slide Rangefinder" disclosed and claimed in U.S. Pat. No. 3,784,305 assigned to the same assignee.
It is well known by those skilled in photographic apparatus art that all optical systems have front and rear nodal points. The above identified patent has described one effective use of the nodal points in a rangefinder apparatus for a camera. One characteristic of such nodal points includes the property that if light rays are directed toward the front nodal point at a given angle relative to the optical axis, the light rays will emerge from the rear nodal point at an equivalent angle. Assuming now an optical system in collimated space, if the lens of the optical system is oscillated about its rear nodal point, the image formed by the light rays will be independent of an unaffected by the angle of oscillation of the lens and will remain stationary in the image plane. However, assuming an optical system in a non-collimated space, if the lens of the optical system is oscillated about its rear nodal point, the image formed by the light rays will not be independent of the angle of oscillation of the lens, but will oscillate in the image plane. When the optical system is in a condition of focus, the image will not oscillate in the image plane. When the optical system is in a condition of out of focus, the image will oscillate in the image plane.